Today, the ACLU, the ACLU of Pennsylvania, and the NAACP filed a lawsuit against the City of Philadelphia, which violated the First Amendment when it refused to accept an NAACP advertisement in the city's airport. The ad is part of a campaign to promote changes in the criminal justice and education systems. The lawsuit also names as a defendant Clear Channel Outdoor, which handles advertising for the airport.

Here's the rejected ad:

Philadelphia officials now claim that the NAACP's advertisement was rejected because the city-run airport doesn't accept any political, advocacy, or issue-oriented ads. However, the airport has previously allowed a variety of ads that fall squarely in this category. A few examples include:

An ad for the World Wildlife Federation with a picture of two overheated polar bears, reading "WWF is developing global solutions to reduce carbon emissions and helping vulnerable communities, species and habitats adapt to a changing climate"

An ad by the National Center for Missing & Exploited Children concerning places where sexual predators can be found, and discussing dangers the Internet can pose for children

An ad from the Foundation for a Better Life, a group that seeks to "provide good role models, better values and a better life." The ad features a photo of Archbishop Desmond Tutu and reads, "His moral compass points to equality. PEACE. Pass It On."

The First Amendment prohibits the government from favoring some viewpoints over others, which is exactly what Philadelphia did here. Once a government-run airport begins to accept political, issue-oriented ads, it cannot allow some groups to participate in that forum while arbitrarily denying others the same opportunity.

The rejected ad is part of an NAACP public awareness campaign for its "Misplaced Priorities" report, which examines the correlation between high incarceration rates and poor public school performance. Philadelphia is one of the cities profiled in the report, which notes that more than 65 percent of the city's lowest-performing schools are in neighborhoods with the highest incarceration rates. Mass incarceration is also an issue that the ACLU is working to address.

Philadelphia must recognize that the walls of its airport are public space, open to all. As Chris Hansen, senior staff attorney for the ACLU's Speech, Privacy and Technology Project puts it, "The government cannot pick and choose which speech it deems acceptable and which it does not."

Travelers arriving in America know that freedom of speech is one of our most fundamental values. Let's show them that we mean it.